Dietary beta-carotene absorption and metabolism in ferrets and rats

The ability of the ferret (Mustela putorius furo) to absorb dietary beta-carotene was studied to determine its appropriateness as a laboratory animal model for studies on beta-carotene metabolism. At baseline, the mean serum beta-carotene level in ferrets was 0.6 micrograms/dl and no beta-carotene was present in liver or adipose tissue. After the ferrets were fed 4 or 20 mg of beta-carotene/kg body wt daily for 2 wk, serum levels were 15.3 and 41.5 micrograms/dl, liver values were 0.9 and 4.1 micrograms/g and adipose tissue values were 0.1 and 0.2 microgram/g of beta-carotene, respectively. Thus, like humans, ferrets are able to absorb dietary beta-carotene intact. Further, these animals can store quantifiable amounts of dietary beta-carotene in their liver and, to a lesser extent, in adipose tissue. In contrast, serum beta-carotene levels in rats fed the two levels of beta-carotene were very low (0.5 to 0.6 microgram/dl) and no beta-carotene was found in liver or adipose tissue. Thus, the ferret is a more appropriate animal model for studying the intestinal absorption of beta-carotene and its storage and metabolism in body tissues.     

Disease manifestations of canine distemper virus infection in ferrets are modulated by vitamin A status

The measles virus (MV) causes half a million childhood deaths annually. Vitamin A supplements significantly reduce measles-associated mortality and morbidity. The mechanisms whereby vitamin A acts against MV are not understood and currently there is no satisfactory small animal model for MV infection. We report on the development of a ferret model to study antiviral activity of vitamin A against canine distemper virus (CDV). CDV is closely related to MV at the molecular level and distemper in ferrets mimics measles in humans. We infected vitamin A-replete (control) and vitamin A-depleted ferrets with CDV and assessed the ability of high-dose vitamin A supplements to influence CDV disease. In control ferrets, CDV infection caused fever, rash, conjunctivitis, cough, coryza, and diarrhea. In contrast, control ferrets that were given 30 mg of vitamin A did not develop typical distemper after infection and exhibited only a mild rash. The supplement did not negatively affect ferret health and resulted in a 100% increase in serum and liver vitamin A concentrations. We also found that profound vitamin A deficiency is inducible in ferrets and can be rapidly reversed upon high-dose vitamin A supplementation. Vitamin A deficiency caused anorexia, diarrhea, cataracts, behavioral abnormalities, and ultimately death, with or without CDV infection. All ferrets that received vitamin A supplements, however, recovered uneventfully from CDV infection. These results replicate many aspects of the observations of vitamin A therapy in humans with measles and suggest that CDV infection in ferrets is an appropriate model for the study of the antiviral mechanism of vitamin A.     

The relative vitamin A value of 9-cis beta-carotene is less and that of 13-cis beta-carotene may be greater than the accepted 50% that of all-trans beta-carotene in gerbils

The effectiveness of beta-carotene (betaC) as a vitamin A (VA) precursor may be influenced by the proportions of cis isomers of betaC consumed in the diet. Although the metabolic fates of cis isomers of betaC are poorly understood, their retinol equivalency has been assigned a value 50% that of all-trans (at) betaC. A dose-response design was used to estimate the relative VA value (VAV) of atbetaC, 9-cis (9c) betaC and 13-cis (13c) betaC in gerbils using total liver retinol as a measure of VAV. Ten groups of gerbils received a daily dose of oil with or without betaC isomer by gavage for 7 d. Nine groups (n = 5) were divided equally among the three betaC dosing treatments with each isomer provided at 141, 275 and 418 nmol/d. Total liver VA (171-259 nmol) in gerbils administered atbetaC was higher than total liver betaC (25-53 nmol). Stores of VA and betaC in livers from gerbils administered atbetaC were higher than stores of VA and betaC in livers from those given 9cbetaC or 13cbetaC. The relative VAV of cis betaC isomers was estimated by comparing slopes of dose-response lines of all three betaC isomers using atbetaC as a reference. Total liver VA and betaC increased linearly (P < 0.05) with increasing betaC intake in gerbils gavaged with all three betaC isomer oils. The relative VAV of 9cbetaC was less (38%) and 13cbetaC was more (62%) than the assigned value of 50% that of atbetaC. Thus, the proportions of cis isomers of betaC contained in a food could negatively affect the vitamin A value of the diet.     

Amount of dietary fat and type of soluble fiber independently modulate postabsorptive conversion of beta-carotene to vitamin A in mongolian gerbils

Current dietary guidelines recommend a decrease in fat intake and an increase in fiber consumption. Decreased bioavailability (BV) of carotenoids is thought to be associated with both of these recommendations. A 2 x 4 factorial design was used to test the effects of dietary fat level at 10 or 30% of total energy and fiber type using no fiber, silica, citrus pectin or oat gum (7 g/100 g) on beta-carotene (betaC) BV in 4- to 5-wk-old Mongolian gerbils. We assessed BV as both accumulation of betaC and bioconversion of betaC to vitamin A (VA) in tissues. A VA- and betaC-deficient diet was fed for 1 wk followed by one of eight isocaloric, semipurified diets supplemented with carrot powder [ approximately 1 microgram betaC, 0.5 microgram alpha-carotene (alphaC)/kJ diet] for 2 wk (n = 12/group). Increasing dietary fat resulted in higher VA (P: = 0.074) and lower betaC (P: = 0.0001) stores in the liver, suggesting that consumption of high fat diets enhances conversion of betaC to VA. The effect of soluble fiber on hepatic VA storage was dependent on fiber type. Consumption of citrus pectin resulted in lower hepatic VA stores and higher hepatic betaC stores compared with all other groups, suggesting less conversion of betaC to VA. In contrast, consumption of oat gum resulted in hepatic VA and betaC stores that were higher (P = 0.012) and lower (P = 0.022), respectively, than those of citrus pectin-fed gerbils. The level of dietary fat consumed with soluble fiber had no interactive effects on hepatic VA, betaC or alphaC stores. Results demonstrate that betaC BV is independently affected by dietary fat level and type of soluble fiber, and suggest that these dietary components modulate postabsorptive conversion of betaC to VA. This study confirms the negative effects of citrus pectin on betaC BV, and suggests that oat gum does not adversely affect betaC BV.     

All-trans beta-carotene appears to be more bioavailable than 9-cis or 13-cis beta-carotene in gerbils given single oral doses of each isomer

Male gerbils (28 d old) were used to investigate the beta-carotene (betaC) isomer pattern in the intestine and tissues 6 h after ingestion of three betaC isomers. After a 49- to 52-d period of consuming the AIN93G diet without vitamin A (VA) or betaC, three groups (n = 7) were gavaged with crystalline all-trans (at)betaC, 9-cis (9c)betaC or 13-cis (13c)betaC solubilized in oil and a control group (n = 5) with oil alone. Total betaC per dose for gerbils in the atbetaC, 9cbetaC and 13cbetaC groups was 384 +/- 3, 391 +/- 2 and 386 +/- 2 nmol, respectively. After 6 h, gerbils were killed and serum, stomach contents, small intestinal contents (SIC), small intestinal mucosal scrapings (SIM) and liver were collected. betaC and VA in tissues were quantified using HPLC. Nonspecific isomerization of betaC occurred in the digestive tracts of gerbils administered betaC; the greatest effect was in the SIC of the 13cbetaC (50:50 cis:trans) and 9cbetaC (70:30 cis:trans) groups. Concentrations of total betaC in the SIM of gerbils administered at betaC were greater than those intubated with 9cbetaC and 13cbetaC (P < 0.05). Gerbils that received atbetaC had greater total betaC concentrations in serum (P < 0.05) and total betaC stores in liver (P < 0.01) compared with those administered 9cbetaC and 13cbetaC. Gerbils intubated with 9cbetaC had higher levels of total betaC in serum (P = 0.05) and liver (P < 0.01) compared with those intubated with 13cbetaC. Because of its preferential uptake, transport and tissue accumulation, atbetaC appears to be a more bioavailable isomer than 9cbetaC or 13cbetaC in gerbils.     

Evaluation of the preruminant calf as a model for the study of human carotenoid metabolism.

This study evaluated the preruminant calf as an animal model for the study of human carotenoid metabolism. Fifteen newborn male Holstein calves were fed a carotenoid-free milk replacer diet to maintain them in the preruminant state. After a 7-d adjustment period, three calves were killed and 12 calves received a single oral dose (20 mg) of beta-carotene in the form of water-soluble beadlets. Blood samples were collected periodically and samples of various tissues were collected when the calves were killed. Three animals each were killed by exsanguination at 1, 3, 6 and 11 d post-dosing. Serum beta-carotene concentrations peaked between 12 and 30 h post-dosing and declined slowly afterwards. Serum data were fitted to a two-compartment model and yielded an elimination constant (k2) that was similar to reported human values. Adrenal tissue showed significant concentrations of beta-carotene by 24 h post-dosing, and levels were still elevated at 264 h. Liver, spleen and lung beta-carotene concentrations were significantly elevated by 24 h and rapidly declined thereafter. Adipose and kidney peak beta-carotene concentrations were observed at 72 and 144 h, respectively. Heart and muscle did not display significant changes in beta-carotene concentrations. The preruminant calf shows promise as an animal model for the study of absorption and metabolism of carotenoids by humans.     

Beta-carotene micellarization during in vitro digestion and uptake by Caco-2 cells is directly proportional to beta-carotene content in different genotypes of cassava

Cassava, a staple food in sub-Saharan Africa, does not provide adequate amounts of pro-vitamin A (VA) carotenoids and has been targeted for biofortification (i.e. selectively breeding cultivars of increased nutrient density with agroeconomically acceptable characteristics). However, the accessibility of pro-VA carotenoids for absorption in different cultivars of cassava remains unknown. Here, we used the coupled in vitro digestion/Caco-2 cell uptake model to screen the relative accessibility of beta-carotene (betaC) in 10 cultivars of cassava with varying concentrations of betaC. After cooking (boiled for 30 min), the betaC concentration in tubers from different cultivars ranged from less than detectable to 6.9 microg betaC/g cassava. Samples were subjected to simulated oral, gastric, and small intestinal digestion to determine stability and micellarization of betaC. All-trans betaC, 9-cis betaC, and 13-cis betaC were the most abundant carotenoids in cooked cassava and recoveries after digestion exceeded 70%. Efficiency of micellarization of total betaC was 30 +/- 2% for various cultivars with no significant difference in isomers and linearly proportional to concentration in cooked cassava (r = 0.87; P < 0.001). Accumulation of all-trans betaC by Caco-2 cells incubated with the diluted micelle fraction for 4 h was proportional (R(2) = 0.99; P < 0.001) to the quantity present in micelles. These results suggest that all-trans betaC content appears to provide the key selection marker for breeding cassava to improve VA status and that the more complicated screening procedure using in vitro digestion coupled to cell uptake does not provide additional information on potential bioavailability.     

Bioavailability of beta-carotene (betaC) from purple carrots is the same as typical orange carrots while high-betaC carrots increase betaC stores in Mongolian gerbils (Meriones unguiculatus)

Vitamin A (VA) deficiency is a worldwide public health problem. Biofortifying existing sources of beta-carotene (betaC) and increasing dietary betaC could help combat the issue. Two studies were performed to investigate the relative betaC bioavailability of a betaC supplement to purple, high-betaC orange, and typical orange carrots using Mongolian gerbils (Meriones unguiculatus). In study 1, which used a traditional bioavailability design, gerbils (n 32) received a diet containing orange, purple, or white carrot powder, or white carrot powder +a betaC supplement. In study 2, which included betaC-biofortified carrots, gerbils (n 39) received orange, high-betaC orange, purple, or white carrot powder in their diet. Both studies lasted 21 d and the gerbils were killed to determine the effect of carrot type or supplement on serum and liver betaC, alpha-carotene, and VA concentrations. Liver stores of betaC or VA in the gerbils did not differ between orange and purple carrot diets when equal amounts of betaC from each of the diets were consumed (P>0.05). Both the orange and purple carrot diet resulted in higher liver VA compared with the supplement (P<0.05). High-betaC carrots resulted in more than 2-fold higher betaC and 1.1 times greater VA liver stores compared with typical orange carrots (P<0.05). These results suggest that high-betaC carrots may be an alternative source of VA to typical carrots in areas of VA deficiency. Second, phenolics including anthocyanins and phenolic acids in purple carrot do not interfere with the bioavailability of betaC from purple carrots.     

Novel lycopene metabolites are detectable in plasma of preruminant calves after lycopene supplementation

Appropriate animal models such as preruminant calves are necessary to study the complex physiological functions of carotenoids and to relate them to possible health effects in humans. In this study, the bioavailability and metabolism of lycopene from 2 dietary supplements were compared. LycoVit containing synthetic lycopene and Lyc-O-Mato containing natural tomato oleoresin were administered to 2 groups of preruminant calves (each n = 8) for 14 d in daily doses of 15 mg of lycopene. Plasma was analyzed for carotenoids before the intervention period, directly after, and each day for 5 d after the end of the intervention. All-trans and 5-cis lycopene, and 3 lycopene metabolites not previously found in calf plasma were detected. These metabolites contributed 52% of the total lycopene content measured at the end of the intervention period. Based on spectroscopic data, they might be hydrogenation products, which are formed from all-trans and/or 5-cis lycopene. In the LycoVit group, total lycopene concentrations were approximately 300% higher (286 +/- 89 nmol/L) than in the Lyc-O-Mato group (72 +/- 33 nmol/L) (P < 0.001). This indicates that, unlike in humans, lycopene from LycoVit and Lyc-O-Mato does not have equal bioavailabilities in preruminant calves. Therefore, the preruminant calf may not be a suitable animal model with which to study the biological and physiological effects of lycopene.     

Nutritional aspects of phytoene and phytofluene, carotenoid precursors to lycopene

Epidemiological studies suggest an inverse relationship between tomato consumption and serum and tissue lycopene (LYC) levels with risk of some chronic diseases, including several cancers and cardiovascular disease. LYC, the red carotenoid found in tomatoes, is often considered to be the primary bioactive carotenoid in tomatoes that mediates health benefits, but other colorless precursor carotenoids, phytoene (PE) and phytofluene (PF), are also present in substantial quantities. PE and PF are readily absorbed from tomato foods and tomato extracts by humans. Animal models of carotenoid absorption suggest preferential accumulation of PE and PF in some tissues. The reasonably high concentrations of PE and PF detected in serum and tissues relative to the concentrations in foods suggest that absorption or metabolism of these compounds may be different from that of LYC. Experimental studies, both in vitro and in vivo, suggest that PE and PF exhibit bioactivity but little is known about their impact in humans. Methods for producing isotopically labeled PE, PF, and LYC tracers from tomato plant cell culture offer a unique tool for further understanding the differential bioavailability and metabolism of these 3 prominent tomato carotenoids and how they may affect health.     

Absorption and conversion of 11,12-(3)H-beta-carotene to vitamin A in Sprague-Dawley rats of different vitamin A status

The aim of this study was to determine the bioavailability and bioconversion to vitamin A of a single oral dose in oil or an aqueous dispersion of labeled beta-carotene in rats of different vitamin A status. Weanling Sprague-Dawley rats were fed a vitamin A-deficient diet and supplemented for 4 wk with 0, 7, 21 and 63 micro g/(rat. d) of retinyl acetate. The rats, of different vitamin A status, were then given a single oral dose of 11,12-(3)H-beta-carotene (0.15 micro mol) dissolved in corn oil or dispersed in aqueous Tween 80. The rats were killed 4 or 24 h after the dose, and serum, liver, the entire digestive tract, other tissues, urine and feces were analyzed for carotenoids, retinoids and associated radioactivity. At 4 h after the dose, 85 +/- 9% of the administered radioactivity was recovered. Almost 50% of the dose was present as intact beta-carotene in the large intestine where further absorption and conversion was ruled out. The absorption of beta-carotene was very low, and < 5% of the radioactive dose was converted to retinoids. The absorption and conversion to vitamin A did not differ among rats of different vitamin A status. The results suggest that a single oral dose of beta-carotene might not be an effective way of raising vitamin A stores in the body.     

Mongolian gerbils can utilize provitamin-A carotenoids in deep-fried carrot chips

Deep-fried carrot chips, containing provitamin-A carotenes, were developed as an alternative mode of dietary intervention to combat vitamin A deficiency. The biological use of carotenoids in this product as vitamin A precursors was evaluated in Mongolian gerbils. Male 4-wk-old gerbils were fed a diet containing all essential nutrients for 1 wk. Then six gerbils were killed, and the remaining gerbils were fed the diet without vitamin A for 6 wk to produce marginal vitamin A deficiency. After depletion, six gerbils were killed and the remainder divided into four groups of 12 gerbils each and fed vitamin A-containing diet (+VA), beta-carotene-containing diet (BC), carrot chip-containing diet (CC), or diet containing no vitamin A/provitamin-A carotenes (-VA). The first three diets contained approximately 6 microg RE/g. Six gerbils from each group were killed after 2 wk of consuming these diets, and 6 after 4 wk. Final body weight and weekly food consumption did not differ among groups after 2 or 4 wk of repletion. Total liver vitamin A stores of BC and CC gerbils killed after 4 wk of repletion were not different from those of gerbils killed before depletion, but those of -VA gerbils were significantly lower (P < 0.05) and those of +VA gerbils were significantly higher (P < 0.05). Plasma retinol levels of gerbils killed after 4 wk of repletion, including the -VA group, did not differ. Total liver alpha- and beta-carotenes and 9-cis beta-carotene contents of the CC group were significantly higher (P < 0.05) than in the BC group after 4 wk of repletion. This carrot chip product effectively reversed vitamin A deficiency in gerbils.     

Taurocholate stimulates the absorption and biotransformation of β‐carotene in intact and lymph duct‐cannulated ferrets

We have determined the influence of dietary taurocholate and β‐carotene on the absorption and biotransformation of newly administered β‐[¹⁴C]carotene. Male ferrets were fed the control or β‐carotene diet (0.05% β‐carotene wt/wt) with and without taurocholate (1% wt/wt) for four weeks, and then the absorption and biotransformation of newly administered β‐[¹⁴C]carotene was measured after eight hours in intact or thoracic lymph duct‐cannulated animals. Percent recovery of β‐[¹⁴C]carotene in the liver was increased 3.6‐fold (p < 0.05) in the taurocholate‐fedferrets regardless of whether they were fed the control or β‐carotene diet. Percent recovery of labeled vitamin A in the liver was also increased by the same magnitude (p < 0.05). These results were confirmed in thoracic lymph duct‐cannulated ferrets. The recoveries of β‐carotene label in the lymph were comparable to the corresponding values in livers of intact animals. The recovery of β‐carotene label in the liver was 50% (p < 0.05) higher in β‐carotene‐fed than in control animals. Taurocholate stimulates intestinal absorption of newly administered β‐[¹⁴C]carotene and its metabolic conversion to ¹⁴C‐labeled vitamin A (retinol + retinyl ester) 3.6‐fold. β‐Carotene absorption is as efficient in thoracic lymph duct‐cannulated ferrets as in intact animals. Prior β‐carotene feeding also stimulates the absorption of newly administered β‐carotene by 50%.     

Beta-carotene and other carotenoids as antioxidants.

Carotenoids are natural pigments which are synthesized by plants and are responsible for the bright colors of various fruits and vegetables. There are several dozen carotenoids in the foods that we eat, and most of these carotenoids have antioxidant activity. Beta-carotene has been best studied since, in most countries it is the most common carotenoid in fruits and vegetables. However, in the U.S., lycopene from tomatoes now is consumed in approximately the same amount as beta-carotene. Antioxidants (including carotenoids) have been studied for their ability to prevent chronic disease. Beta-carotene and others carotenoids have antioxidant properties in vitro and in animal models. Mixtures of carotenoids or associations with others antioxidants (e.g. vitamin E) can increase their activity against free radicals. The use of animals models for studying carotenoids is limited since most of the animals do not absorb or metabolize carotenoids similarly to humans. Epidemiologic studies have shown an inverse relationship between presence of various cancers and dietary carotenoids or blood carotenoid levels. However, three out of four intervention trials using high dose beta-carotene supplements did not show protective effects against cancer or cardiovascular disease. Rather, the high risk population (smokers and asbestos workers) in these intervention trials showed an increase in cancer and angina cases. It appears that carotenoids (including beta-carotene) can promote health when taken at dietary levels, but may have adverse effects when taken in high dose by subjects who smoke or who have been exposed to asbestos. It will be the task of ongoing and future studies to define the populations that can benefit from carotenoids and to define the proper doses, lengths of treatment, and whether mixtures, rather than single carotenoids (e.g. beta-carotene) are more advantageous.     

β-Carotene and Other Carotenoids as Antioxidants

Carotenoids are natural pigments which are synthesized by plants and are responsible for the bright colors of various fruits and vegetables. There are several dozen carotenoids in the foods that we eat, and most of these carotenoids have antioxidant activity. β-carotene has been best studied since, in most countries it is the most common carotenoid in fruits and vegetables. However, in the U.S., lycopene from tomatoes now is consumed in approximately the same amount as β-carotene. Antioxidants (including carotenoids) have been studied for their ability to prevent chronic disease. β-carotene and others carotenoids have antioxidant properties in vitro and in animal models. Mixtures of carotenoids or associations with others antioxidants (e.g. vitamin E) can increase their activity against free radicals. The use of animals models for studying carotenoids is limited since most of the animals do not absorb or metabolize carotenoids similarly to humans.

Epidemiologic studies have shown an inverse relationship between presence of various cancers and dietary carotenoids or blood carotenoid levels. However, three out of four intervention trials using high dose β-carotene supplements did not show protective effects against cancer or cardiovascular disease. Rather, the high risk population (smokers and asbestos workers) in these intervention trials showed an increase in cancer and angina cases. It appears that carotenoids (including β-carotene) can promote health when taken at dietary levels, but may have adverse effects when taken in high dose by subjects who smoke or who have been exposed to asbestos. It will be the task of ongoing and future studies to define the populations that can benefit from carotenoids and to define the proper doses, lengths of treatment, and whether mixtures, rather than single carotenoids (e.g. β-carotene) are more advantageous.     

The medical importance of vitamin A and carotenoids (with particular reference to developing countries) and their determination

Vitamin A, or retinol, is an essential nutrient for man and all mammalian species since it cannot be synthesised within the body. Deficiency of the vitamin results in adverse effects on growth, reproduction and resistance to infection. The most important manifestation of severe vitamin A deficiency (VAD) is xerophthalmia, and irreversible blindness may eventually occur in one or both eyes. VAD is still an important micronutrient deficiency problem in many developing countries, afflicting large numbers of pre-school children. It is often associated with protein-energy malnutrition, parasitic infestation and diarrhoeal disease. For many communities in developing countries, the major source of vitamin A in the diet is carotenoids. These compounds are synthesised only by photosynthetic microorganisms and by members of the plant kingdom where they serve important functions in metabolism, including participating in the photosynthetic process. These pigments also provide aesthetic qualities as colourants in the plant and animal kingdoms. Most importantly, the carotenoids serve the animal kingdom as sources of vitamin A activity. Major advances have occurred in understanding the role and mechanisms of action of carotenoids. They are now thought to play specific roles in mammalian tissues related to their function in plants. Carotenoids, with their highly reactive conjugated double bonds, act as free radical traps or antioxidants and may play an important role in the prevention of cancers. In view of the wide medical importance of carotenoids, much attention has been given to the determination of these pigments in foods as well as blood. Carotenoids in foods have conventionally been analysed using the open-column chromatography technique, but the high-pressure liquid chromatographic (HPLC) method is now gaining in importance as well. The classical method for the determination of carotenoids in blood is by the spectrophotometric method while the HPLC method is also recommended for use. An example of an HPLC method developed for the simultaneous determination of retinol and carotenoids in food and blood is given. The determination of retinol and carotenoids should be further developed in view of the wide importance of carotenoids in health and disease.     

The vitamin A spectrum: from deficiency to toxicity

Dark adaptation has been used as a tool for identifying patients with subclinical vitamin A deficiency. With this functional test it was shown that tissue vitamin A deficiency occurs over a wide range of serum vitamin A concentrations. However, serum vitamin A concentrations >1.4 micromol/L predict normal dark adaptation 95% of the time. Other causes of abnormal dark adaptation include zinc and protein deficiencies. Stable isotopes of vitamin A and isotope-dilution techniques were used recently to evaluate body stores of vitamin A and the efficacy of vitamin A intervention programs in field settings and are being used to determine the vitamin A equivalences of dietary carotenoids. Vitamin A toxicity was described in patients taking large doses of vitamin A and in patients with type I hyperlipidemias and alcoholic liver disease. Conversely, tissue retinoic acid deficiency was described in alcoholic rats as a result of hepatic vitamin A mobilization, impaired oxidation of retinaldehyde, and increased destruction of retinoic acid by P450 enzymes. Abnormal oxidation products of carotenoids can cause toxicity in animal models and may have caused the increased incidence of lung cancer seen in 2 epidemiologic studies of the effects of high-dose beta-carotene supplementation. Major issues that remain to be studied include the efficiency of conversion of carotenoids in whole foods to vitamin A by using a variety of foods in various field settings and whether intraluminal factors (eg, parasitism) and vitamin A status affect this conversion. In addition, the biological activity of carotenoid metabolites should be better understood, particularly their effects on retinoid signaling.     

Tissue distribution of lycopene in ferrets and rats after lycopene supplementation

To determine lycopene uptake and tissue distribution in ferrets (Mustela putorius furo) and F344 rats, we supplemented orally 4.6 mg/(kg body wt.d) lycopene in a tomato oleoresin-corn oil mixture (experimental groups). After 9 wk of supplementation, the animals were killed and blood and organs were collected. Plasma and tissue carotenoids were extracted and measured using HPLC. Mean concentrations of lycopene (nmol/kg wet tissue) in saponified tissues of ferrets were as follows: liver 933, intestine 73, prostate 12.7 and stomach 9.3. Levels of lycopene (nmol/kg wet tissue) in saponified tissue of rats were as follows: liver 14213, intestine 3125, stomach 78.6, prostate 24 and testis 3.9. When these organs were extracted without saponification, the lycopene levels were lower, except for rat testis. All-trans-lycopene was the predominant isomer found in tomato oleoresin and in the majority of rat tissues, whereas cis-lycopenes were predominant in rat prostate and plasma. This pattern was reversed in ferrets. The results show the following: 1) lycopene from tomato oleoresin is absorbed and stored primarily in the liver of both animals; 2) saponification generally improves the extraction of lycopene from most tissues of both animals; 3) cis-lycopene and all-trans-lycopene are the predominant isomers in ferret and rat tissues, respectively; and 4) rats absorb lycopene more effectively than ferrets.     

Beta-carotene uptake and tissue distribution in ferrets (Mustela putorius furo).

Ferrets accumulate beta-carotene in liver and adipose tissue after chronic feeding. This study was designed to further evaluate the time course of uptake and depletion of beta-carotene in ferret serum and tissues. Male ferrets (n = 15; 1000-1200 g) were given a single dose of beta-carotene (10 mg/kg body wt) with a meal. Animals were killed at various time points over an 11-d period. Blood and tissue samples were extracted and analyzed for beta-carotene by HPLC. Peak serum beta-carotene levels (0.68 +/- 0.18 mumol/L) were observed 8 h after the test meal. beta-Carotene was essentially cleared from the blood by 76 h. Peak beta-carotene concentrations (nmol/g) were observed between 8 and 16 h after ingestion for liver (1.20 +/- 0.04), lung (0.042 +/- 0.012), kidney (0.090 +/- 0.015) and spleen (0.076 +/- 0.012). Ferret liver also seemed to contain a variety of other polar and nonpolar carotenoids. Ferrets were shown to absorb beta-carotene from a meal and have a consistent serum response pattern. Absorbed beta-carotene is differentially distributed in a variety of tissues. The ferret seems to be a useful model for the study of beta-carotene absorption and metabolism.